Vehicle control system

ABSTRACT

A vehicle control system which controls a vehicle in accordance with the curvature of a road as determined from map information comprising a set of coordinate points which represent the course of the road. A passable vehicle speed enabling the vehicle to pass through a plurality of nodes existing at predetermined distances within an operating section established on the road ahead of a given vehicle position is calculated on the assumption that a voluntary speed reduction has been conducted. The radii of a first virtual turning locus and a second virtual turning locus produced at a predetermined lateral acceleration are calculated based on the passable vehicle speeds at the nodes. A passable zone, a warning zone and an automatic speed-reducing zone are established based on the first and second virtual turning locus radii. If any of the nodes ahead of the virtual vehicle position exists in the warning zone, a warning is provided to the driver. If any of the nodes ahead of the virtual vehicle position exists in the automatic speed-reducing zone, automatic speed reduction of the vehicle is carried out.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vehicle control system which controlsa vehicle according to the course or curvature of a road as determinedon the basis of map information comprised of a set of coordinate pointsrepresenting the road.

2. Description of the Prior Art

There is a known technique disclosed in Japanese Patent ApplicationLaid-open No. 89298/85, which involves evaluating the radius ofcurvature of a curve ahead of a subject vehicle in the direction oftravel based on map data provided by a navigation system. The systemdetermines whether the vehicle can pass through the curve at the currentvehicle speed, and gives a warning to the driver if it is determinedthat the vehicle cannot pass through the curve safely at the currentspeed.

It is often the case that the driver appraises a curve existing ahead ofthe vehicle in the traveling direction by a visual judgment or byprevious experience. Normally, the driver voluntarily performs thespeed-reducing operation required for the vehicle to safely pass througha curve.

However, the known technique determines the advisability of passingthrough a curve on the assumption that, until the vehicle enters thecurve, the driver does not voluntarily reduce speed. Therefore, it isoften the case that a warning and an automatic speed-reduction areconducted earlier than required, resulting in a problem withinterference with the driver's driving operation which is troublesomefor the driver.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide awarning and an automatic speed-reduction with an appropriate timingwhile avoiding interference with the driver's voluntary speed-reductionat a location short of the curve.

To achieve the above object, according to the present invention there isprovided a vehicle control system, comprising: map informationoutputting means for outputting a map comprised of a plurality ofcoordinate points representing a road; vehicle position detecting meansfor detecting a position of a subject vehicle on the map; vehicle speeddetecting means for detecting a vehicle speed; operating-sectioncalculation means for calculating an operating section in which it isdetermined whether the vehicle speed is appropriate based on a detectedvehicle speed; passable vehicle speed calculation means for calculatinga passable vehicle speed at a virtual vehicle position which isestablished in the operating section, based on the detected vehiclespeed and a distance from the vehicle position to the virtual vehicleposition; zone establishing means for establishing a passage determiningzone having the passable vehicle speed as a criterion based on thevirtual vehicle position; passing condition determining means fordetermining a passing condition by comparing the passage determiningzone with a coordinate point located ahead of the virtual vehicleposition within the operating section; and vehicle control means forcontrolling the vehicle based on a result of the determination by thepassing condition determining means.

With the above arrangement, the passage determining zone establishedbased on the passable vehicle speed is compared with the coordinatepoints of the road existing ahead of the virtual vehicle position, andtherefore, the passing condition of the vehicle is accurately determinedto provide a control such as the warning and the automaticspeed-reduction. At that time, the calculation of the vehicle speed isconducted not only based on the detected vehicle speed but also based onthe distance from the vehicle position to the virtual vehicle position.Accordingly, in view of a voluntary vehicle speed-reduction conducted bythe driver before arriving at the virtual vehicle position, it ispossible to avoid the inconvenience of unnecessary warning and automaticspeed reduction.

If the passable vehicle speed calculation means sequentially establishesthe plurality of coordinate points included within the operating sectionin sequence as the virtual vehicle positions, and accurately determinesthe condition of passing through the coordinate points ahead of thevirtual vehicle position, it can be accurately determined whether thevehicle can pass through the coordinate points included within theoperating section.

If the radius of a virtual turning locus of the vehicle is calculatedbased on the passable vehicle speed and the passage determining zone isestablished based on the radius of the virtual turning locus, thepassage determining zone can be accurately determined with a simplecalculation.

If the passable vehicle speed calculating means calculates the passablevehicle speed as a vehicle speed resulting from a speed reductionconducted at a predetermined reference speed-reducing rate from thevehicle position to the virtual vehicle position, it is possible toaccurately calculate the passable vehicle speed by a simple calculation.

If the vehicle control means is a means for providing a warning to thedriver, when it is determined that it is difficult for the vehicle topass through the curve without speed reduction, the driver can beaccurately informed of the determination.

If the vehicle control means is a means for controlling the vehiclespeed, when it is judged that it is difficult for the vehicle to passthrough the curve without speed reduction, the vehicle speed can beautomatically reduced.

If the passage determining zone includes a warning zone to provide awarning to the driver and an automatic speed-reducing zone toautomatically reduce the vehicle speed, it is possible to cope with thedegree of difficulty of passing through the curve.

If the zone establishing means establishes a warning zone and anautomatic speed-reducing zone based on a predetermined reference lateralacceleration, it is possible to accurately establish the warning zoneand the automatic speed-reducing zone.

If the zone establishing means establishes a warning zone and anautomatic speed-reducing zone based on a predetermined referencedeceleration, it is possible to accurately establish the warning zoneand the automatic speed-reducing zone.

The above and other objects, features and advantages of the inventionwill become apparent from the following description of the preferredembodiments taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating the entire arrangement of avehicle control system according to a first embodiment of the presentinvention.

FIG. 2 is a first portion of a flow chart.

FIG. 3 is a second portion of the flow chart of FIG. 2.

FIG. 4 is a diagram illustrating the established condition of zones onthe road.

FIG. 5 is a diagram illustrating the relationship between the road andthe zones at node N_(k).

FIG. 6 is a diagram for explaining the operation of the invention.

FIG. 7 is a diagram for explaining the operation of a second embodimentof the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment of the present invention will now be described withreference to FIGS. 1 to 6.

In FIG. 1, reference character NV represents a navigation system for avehicle. The navigation system NV includes an inertial navigating device3 to which signals from a yaw rate sensor 1 and a vehicle speed sensor 2(vehicle speed detecting means) are supplied, map information outputtingmeans 4 using an IC card or CD-ROM, and map-matching means 5 thatoverlaps a vehicle-traveling locus outputted from the inertialnavigating device 3 and map information outputted from the mapinformation outputting means 4. Also provided is a GPS unit 7 to which asignal from a GPS antenna 6 is supplied, vehicle position detectingmeans 8 for detecting a vehicle position based on the positioncoordinates outputted from the map-matching control means 5 and theposition coordinates outputted from the GPS unit 7, and course searchingmeans 10 for searching the course until the destination based on adestination coordinates signal from the destination inputting means 9and the vehicle position coordinates signal from the vehicle positiondetecting means 8.

Reference character ZD represents a zone determining section. The zonedetermining section includes road data calculation means 11 forcalculating data of a road ahead of the vehicle as coordinates of aplurality of nodes (which will be described hereinafter) based on anoutput from the course searching means 10, and preread distance andstopping distance calculation means 12 for calculating a prereaddistance Sa and a stopping distance Sb (which will be describedhereinafter) based on an output from the vehicle speed sensor 2. Alsoprovided is operating section calculation means 13 for calculating anoperating section A (which will be described hereinafter) based on thecourse as well as the preread distance (Sa) and the stopping distanceSb, passable vehicle speed calculation means 14 for calculating apassable vehicle speed V_(k) (which will be described hereinafter) basedon an output from the vehicle sensor 2, zone establishing means 15 forestablishing a passable zone Z₁, a warning zone Z₂, and an automaticspeed-reducing zone Z₃ (all of which will be described hereinafter)based on the road data and the passable vehicle speeds, and passingcondition determining means 16 for determining whether the nodes of theroad ahead of the subject vehicle exist in which zone Z₁, Z₂, or Z₃, byoverlapping the nodes existing in the operating section A with each ofthe zones Z₁, Z₂, and Z₃. Each of the zones Z₁, Z₂, and Z₃ constitutes apassage determining zone in the present invention.

Connected to the passing condition determining means 16 are alarm orwarning means 17 (vehicle control means) such as a buzzer, a chime and alamp, and automatic speed-reducing means 18 comprising engine outputreducing means or braking means. If the node ahead of the subjectvehicle exists in the warning zone X₃, an alarm is provided to thedriver by the alarm means 17. If the node ahead of the vehicle exists inthe automatic speed-reducing zone Z₃, an automatic speed reduction iscarried out by the automatic speed-reducing means 18.

The operation of the embodiment of the present invention provided withthe above-described arrangement will be described below with referenceto FIG. 1 in combination with the flow chart shown in FIGS. 2 and 3.

First, factors influencing control such as a coefficient of friction ofthe road surface, driver's conditions (driving skill and fatigueconditions), a road gradient, whether it is night or day and the like,are read (at step S1). Then, predetermined reference lateralaccelerations α₁, α₂ and a predetermined reference deceleration β areset based on the various factors (at step S2).

As used herein, symbol α₁ represents a first reference lateralacceleration used for providing the alarm when there is a possibilitythat the vehicle will exceed the lateral acceleration when it is passingthrough a curve. The symbol α₂ represents a second reference lateralacceleration used for conducting the automatic speed-reduction, whenthere is a possibility that the vehicle will exceed the lateralacceleration when the vehicle is passing through a curve. For example,the first reference lateral acceleration α₁ is set in a range of 2-3m/sec², and the second reference lateral acceleration α₂ is set in arange of 4-6 m/sec² (α₂ >α₁). The symbol β represents a referencedeceleration at which the current vehicle speed is reduced by voluntarybraking by the driver.

The values of α₁, α₂, and β are changed based on the factors read atstep S1, such as the coefficient of friction of the road surface, thedriver's conditions, the road gradient, whether it is night or day andthe like. More specifically, when there are adverse conditions such aswhen the coefficient of friction of the road surface is relativelysmall, when the driver's condition is poor, when the road gradient isdownward, and/or when the visibility is poor at night, α₁, α₂, and β areset at smaller values (for the sake of safety) in order to provide thealarm or the automatic speed-reduction early on (for the sake ofsafety).

Then, a vehicle speed V₀ is read from the vehicle speed sensor 2, andthe coordinates P₀ (X₀, Y₀) of a vehicle position (P₀) are read from thevehicle position detecting means in the navigation system NV (at stepS3).

Next, the stopping distance Sb is calculated by the preread distance andstopping distance calculating means (12) (at step S4). The stoppingdistance Sb corresponds to a distance required for the vehicle to bestopped, when the vehicle is decelerated from the current vehicle speedV₀ at the reference deceleration β. Namely, the stopping distance Sb iscalculated according to the equation (1):

    Sb=V.sub.0.sup.2 /2β                                  (1)

Subsequently, the preread distance Sa is calculated by the prereaddistance/stopping distance calculating means 12 (at step 5). When thevehicle is decelerated for a predetermined preread time t from thecurrent vehicle speed V₀ at the reference deceleration β, the prereaddistance Sa corresponds to a distance through which the vehicle travelswithin the preread time t. Namely, the preread distance Sa is calculatedaccording to the following equation (2):

    Sa=V.sub.0 t-(βt.sup.2 /2)                            (2)

Next, the operating section A defined by a preread distance Sa and astopping distance Sb on the road ahead of the vehicle searched by thecourse searching means 10, is calculated by the operating sectioncalculating means 13. At the same time, the coordinates N_(k) (X_(k),Y_(k)) of the nodes N_(k) (k=1, 2, 3 . . . n) established on the road inthe operating section A is calculated by the road data calculating means(11) (at step S6).

Then, the distances S_(k) between the vehicle position P₀ (X₀, Y₀) andthe nodes N_(k) (X_(k), Y_(k)) are calculated (at step S7).

Then, when the speed reduction is carried out from the current vehiclespeed V₀ at the reference deceleration β in the vehicle position P₀ (X₀,Y₀) until the vehicle arrives at each node N_(k) (X_(k), Y_(k)), thepassable vehicle speed V_(k) (k=1, 2, 3 . . . n) at each of the nodesN_(k) (X_(k), Y_(k)) is calculated (at step S8). Namely, the distance Sk(k=1, 2, 3 . . . n) is provided according to the following equation (3):

    S.sub.k =(V.sub.0.sup.2 -V.sub.k.sup.2)/2β            (3)

Therefore, the passable vehicle speeds V_(k) are calculated from thefollowing equation (4):

    V.sub.k =(V.sub.0.sup.2 -2βS.sub.k).sup.1/2           (4)

Then, the road course within the stopping distance Sb is determinedbased on road data from the road data calculating means 11 (at step S9).If a curve exists within the stopping distance Sb (step S10), apreliminary notice of the curve is provided by the alarm or warningmeans (17) such as a lamp (at step S11).

Next, the nearest node N₁ existing within the operating section A ischosen as the virtual vehicle position N₁ by the zone establishing means15. At the same time, the radius R₁ of first virtual turning loci andthe radius R₂ of each of second virtual turning loci at all the nodes N₂. . . existing at the virtual vehicle position N₁ and within theoperating section A ahead of the virtual vehicle position N1 arecalculated based on the passable vehicle speed V_(k) and the first andsecond standard lateral acceleration α₁, α₂ at each of nodes N_(k)according to the following equations (5) and (6) (at step S12):

    R.sub.1 =V.sub.k.sup.2 /α.sub.1                      (5)

    R.sub.2 =V.sub.k.sup.2 /α.sub.2                      (6)

The first virtual turning locus radius R₁ is the radius of a turninglocus along which the vehicle can pass through a curve at the firstreference lateral acceleration α₁, when the vehicle enters the curve atthe passable vehicle speed V_(k), and the second virtual turning locusradius R₂ is the radius of a turning locus along which the vehicle canpass through a curve at the second reference lateral acceleration α₂,when the vehicle enters the corner at the passable vehicle speed V_(k).

Next, a pair of left and right circular arcs C₁, C₁ having the firstvirtual turning locus radius R₁ calculated at step S12 and a pair ofleft and right circular arcs C₂, C₂ having the second virtual turninglocus radius R₂ also calculated at step S12 are described so that theyare tangent to left and right opposite sides of the road at each nodeN_(k) (at step S13). As a result, the circular arcs C₁, C₁ and circulararcs C₂, C₂ are described on the left and right opposite sides at eachnode N_(k), as illustrated in FIG. 4, and the farther away from thevehicle position P₀ forwardly in an advancing direction, the radii ofcircular arc C₁, C₁ and C₂, C₂ (namely, the first virtual turning locusradius R₁ and the second virtual turning locus radius R₂) are smaller.

Then, the passable zone Z₁, the warning zone Z₂ and the automaticvehicle speed-reducing zone Z₃ which are demarcated by the four circulararcs C₁, C₁, and C₂, C₂, are established by the zone establishing means15 (at step S14). As illustrated in FIG. 5, the passable zone Z₁ isestablished in front of the pair of circular arcs C₁, C₁ ; the warningzone Z₂ is established in the area between the pair of circular arcs C₁,C₁ and the pair of circular arcs C₂, C₂ ; and the automaticspeed-reduction zone Z₃ is established in the area in the rear of thepair of circular arcs C₂, C₂.

Then, the nearest node N₁ in the operating section A is firstestablished as a virtual vehicle position, and it is determined whetherthe nodes N₂, N₃, N₄. . . N_(n) existing forwardly of the nearer node N₁are in which zone Z₁, Z₂ or Z₃. This operation is carried out at all thevirtual vehicle positions N₁, to N_(n), while sequentially displacingthe virtual vehicle position from the nearest node N1 to the farthestnode N_(n) (at step S15). For example, in FIG. 5 the node N_(k) isestablished as the virtual vehicle position. In the road shown by asolid line, the nodes N_(k+1), N_(k+2) and N_(k+3) in front of thevirtual vehicle position N_(k) are in the passable zone Z₁. In the roadshown by a dashed line, the nodes N_(k+1), N_(k+2) and N_(k+3) in frontof the virtual vehicle position N_(k) are in the warning zone Z₂.

However, if the answer at step S16 is "YES", i.e., if the ahead nodesN_(k+1), N_(k+2) . . . N_(n) are in the passable zone Z₁ for all thevirtual vehicle positions N_(k), then it is decided that the vehicle canpass through a curve determined at step S9 at an appropriate speed (atstep S17), returning to step S3.

On the other hand, if the answer at step 16 is "NO", i.e., if any of thenodes N_(k+1), N_(k+2) . . . N_(n) ahead of the virtual vehicle positionN_(k) is in the warning zone Z₂ or in the automatic speed-reducing zoneZ₃, then a warning or alarm is provided to the driver by operating thewarning or alarm means 17 (at step S18).

Further, it is determined for any virtual position N_(k) whether any ofthe nodes N_(k+1), N_(k+2) . . . N_(n) ahead of the virtual vehicleposition N_(k) is in the automatic speed-reducing zone Z₃ (at step S19).If the answer is "NO", i.e., if any of the nodes N_(k+1), N_(k+2) . . .N_(n) is not in the automatic speed-reducing zone Z₃, the processing isreturned to step S3. If the answer at step S19 is "YES", i.e., if any ofnodes N_(k+1), N_(k+2) . . . N_(n) is in the automatic speed-reducingzone Z₃, then the automatic speed reduction means 18 is operated toperform the automatic speed reduction (at step S20).

The above-mentioned operation will further be described with referenceto FIG. 6.

The second virtual turning locus radius R₂ calculated by the equation(6) assumes the largest value in an entrance of the operating section A,and becomes "0 (zero)" at the exit point of the operating section A atwhich the vehicle stops. Accordingly, the automatic speed reducing zoneZ₃ is of a tapered triangular shape. Also, the first virtual turninglocus radius R₁ calculated by the equation (5) assumes the largest valueat the entrance of the operating section A, and becomes "0 (zero)" atthe exit point of the operating section A at which the vehicle stops,and R₁ >R₂. Therefore, the alarming or warning zone Z₂ is of a taperedtriangular shape extending on opposite sides of the automatic speedreducing zone Z₃. An area out of the alarming zone Z₂ and the automaticspeed reducing zone Z₃ is the passable zone Z₁.

On the other hand, in FIG. 6, if it is supposed that, for example, acurve having a radius R of curvature exists within the operating sectionA on the road, then a point "a" at which a straight line representing acurve having the radius R of curvature intersects an outer border of thewarning zone Z₂ is a warning start point. When the curve approaches thewarning start point, a warning is provided. Also, a point "b" at whichthe straight line intersects an outer border of the speed reducing zoneZ₃ is an automatic speed-reduction start point. When the curveapproaches the automatic speed-reduction start point, the speedreduction is started. Accordingly, if a curve has a radius R ofcurvature larger than the largest first virtual turning locus radius R₁at the entrance into the operating section A, a straight linerepresenting the curve having the radius R of curvature doesn'tintersect the warning zone Z₂ nor the automatic speed reducing zone Z₃,and neither the warning nor the automatic speed reduction are performed.

As described above, the passable vehicle speed V_(k) is calculated onthe assumption that voluntary braking at a point short of the curve ispredicted by the driver's visual viewing or experience, and the speed ofthe vehicle is reduced at the reference deceleration β previously set bythe voluntary braking. Therefore, the passable vehicle speed V_(k) islower at the point farther away from the vehicle position. Accordingly,the zone Z₁, Z₂ and Z₃ established based on the passable vehicle speedV_(k) are also determined with the driver's voluntary braking taken intoconsideration. This makes it possible to avoid the warnings and theautomatic speed reduction otherwise unnecessarily frequently provided bythe warning means 17 and the automatic speed reduction means (18),respectively, and to provide only the necessary warning and theautomatic speed reduction at a minimum.

A second embodiment of the present invention will now be described withreference to FIG. 7.

In the second embodiment, in place of the reference deceleration β inthe first embodiment, a first reference deceleration β₁ and a secondstandard deceleration β₂ are established. The passable vehicle speedV_(k) at each node N_(k) calculated at step S8 in the flow chart shownin FIG. 2 is set at two values in correspondence to the first referencedeceleration β₁ and the second reference deceleration β₂ (β₂ >β₁). Morespecifically, the first passable vehicle speed V_(k1) corresponding tothe first reference deceleration β₁ is calculated according to thefollowing equation (7):

    V.sub.k1 =(V.sub.0.sup.2 -2β.sub.1 S.sub.k).sup.1/2   (7)

The second passable vehicle speed V_(k2), corresponding to the secondreference deceleration β₂ is calculated by the following equation (8):

    V.sub.k2 =(V.sub.0.sup.2 -2β.sub.2 S.sub.k).sup.1/2   (8)

Then, the first virtual turning locus radius R₁ for determining theouter border of the warning zone Z₂ for providing a warning iscalculated using the first reference lateral acceleration α₁ and thefirst passable speed V_(k1) according to the following equation (9):

    R.sub.1 =V.sub.k1.sup.2 /α.sub.1                     (9)

The second virtual turning locus radius R₂ for determining the outerborder of the automatic speed reducing zone Z₃ for performing theautomatic speed reduction is calculated using the second referencelateral acceleration α₂ and the second passable vehicle speed V_(k2)according to the following equation 10):

    R.sub.2 =V.sub.k2.sup.2 /α.sub.2                     (1)

It is clear from a comparison of FIGS. 6 and 7 that the warning zone Z₂in the second embodiment (see FIG. 7) is wider than the warning zone inthe first embodiment. Thus, the time from the warning provided up to thestart of the automatic speed reduction is adequately assured and thedriver is afforded sufficient time for braking on his own.

Although the embodiments of the present invention have been described indetail, it will be understood that the present invention is not limitedto the above-described embodiments, and various modifications in designmay be made without departing from the spirit and scope of the inventiondefined in the appended claims.

What is claimed is:
 1. A vehicle control system, comprising:mapinformation outputting means for outputting a map comprised of aplurality of coordinate points representing a road; vehicle positiondetecting means for detecting a position of a vehicle on said map;vehicle speed detecting means for detecting a vehicle speed;operating-section calculation means for calculating an operating sectionin which it is determined whether said detected vehicle speed isappropriate while driving in said operating section; passable vehiclespeed calculation means for calculating a passable vehicle speed at avirtual vehicle position which is established in said operating section,based on said detected vehicle speed and a distance from said vehicleposition to said virtual vehicle position; zone establishing means forestablishing a passage determining zone having said passable vehiclespeed as a criterion based on said virtual vehicle position; passingcondition determining means for determining a passing condition bycomparing said passage determining zone with a coordinate point locatedahead of said virtual vehicle position within said operating section;and vehicle control means for controlling said vehicle based on a resultof the determination by said passing condition determining means.
 2. Avehicle control system according to claim 1, wherein:said passablevehicle speed calculation means sequentially establishes a plurality ofsaid coordinate points included within said operating section as virtualvehicle positions, and determines said passing condition when passingthrough the coordinate points ahead of said virtual vehicle position. 3.A vehicle control system according to claim 1, wherein:said zoneestablishing means calculates a radius of a virtual turning locus ofsaid vehicle based on said passable vehicle speed, and establishes saidpassage determining zone based on the calculated radius of said virtualturning locus.
 4. A vehicle control system according to claim 1,wherein:said passable vehicle speed calculating means calculates saidpassable vehicle speed as a vehicle speed which is obtained on anassumption that a speed reduction is conducted at a predeterminedreference speed-reducing rate from the vehicle position to said virtualvehicle position.
 5. A vehicle control system according to claim 1,wherein:said vehicle control means comprises a means for providing awarning to a driver of said vehicle.
 6. A vehicle control systemaccording to claim 1, wherein:said vehicle control means comprises ameans for controlling the speed of said vehicle.
 7. A vehicle controlsystem according to claim 1, wherein:said passage determining zoneincludes a warning zone for providing a warning to a driver of saidvehicle and an automatic speed-reducing zone for automatically reducingthe speed of said vehicle.
 8. A vehicle control system according toclaim 7, wherein:said zone establishing means establishes said warningzone and said automatic speed-reducing zone based on a predeterminedreference lateral acceleration.
 9. A vehicle control system according toclaim 7, wherein:said zone establishing means establishes said warningzone and said automatic speed-reducing zone based on a predeterminedreference deceleration.